The invention relates to a plasma display screen comprising a carrier plate, a transparent front plate, a ribbed structure which divides the space between the carrier plate and the front plate into plasma cells, which are filled with a gas, and comprising one or more electrode arrays to generate corona discharges in the plasma cells, and comprising a phosphor layer.
The basic principle of a plasma display screen consists in that crossed electrode strips form a matrix, and a gas discharge taking place between them causes pixels to light up. The monochrome versions of the first plasma display screens used the generated light directly. However, as a result of the orange-red color caused by the neon-gas filling, these display screens never became popular and were used only in a very specific market, where there immunity against high magnetic interference fields, mechanical vibrations and extreme temperatures is important, such as in military applications, medical applications, such as NMR diagnostics, and in industrial applications, such as aluminium electrolyses and power stations.
Currently, the color versions of the plasma display screens are much more successful than the old monochrome plasma display screens. In the color versions, the gas filling is an inert gas, for example xenon, or an inert gas mixture, for example a mixture of helium, neon and xenon. In the discharge, ultraviolet radiation is formed in the VUV range i.e. the radiation has a wavelength below 200 nm. This UV radiation excites the phosphors in the phosphor layer arranged in stripes, causing visible light to be emitted in red, green and blue. Consequently, unlike conventional phosphor lamps, the luminescent materials in plasma displays use the high-energy side of the UV spectrum. Dependent upon the composition of the inert gas mixture and the gas pressure, the VUV emission can vary between a single line at 147 nm and a wide band near 172 nm. This leads to new requirements to be met by RGB phosphors in a plasma display. The RGB phosphors form the last member of the energy transfer chain in which electric energy is converted into visible light in the plasma display screen. The efficiency of a plasma display screen comprising a phosphor layer is decisively determined by how completely the generated UV light is absorbed in the phosphor and how completely the generated visible light subsequently leaves the plasma display screen in the direction of the observer.
It has been found that the electro-optical efficiency of conventional red phosphors, for example Y2O3:Eu or Y2O2S:Eu, is unsatisfactory in a plasma display screen because these red phosphors only slightly absorb radiation having a wavelength below 200 nm.
U.S. Pat. No. 4,085,350 discloses a light-emitting component comprising a europium-activated yttrium-gadolinium-borate of the general formula {[(Y1-xGdx)1-zBz]1-yEuy}2O3, where 0xe2x89xa6xxe2x89xa61, 0.001xe2x89xa6yxe2x89xa60.1, 0.25xe2x89xa6zxe2x89xa60.75, as the phosphor, which is excited by the VUV radiation of a gas discharge. This phosphor has an improved quantum yield for the VUV radiation having a wavelength X in the range between 10 and 200 nm.
However, a drawback of these phosphors for generating red radiation resides in that their color point does not lie within the EBU zone for red phosphors, but instead has shifted towards the orange range.
Therefore, it is an object of the invention to provide a plasma display screen comprising a carrier plate, a transparent front plate, a ribbed structure, which divides the space between the carrier plate and the front plate into plasma cells, which are filled with a gas, and comprising one or more electrode arrays for generating corona discharges in the plasma cells, and comprising a phosphor layer, which plasma display screen is characterized by an improved, faithful color rendition and a greater brightness.
In accordance with the invention, this object is achieved by a plasma display screen comprising a carrier plate, a transparent front plate, a ribbed structure which divides the space between the carrier plate and the front plate into plasma cells, which are filled with a gas, and comprising one or more electrode arrays for generating corona discharges in the plasma cells, and comprising a phosphor layer which includes a phosphor selected from the group formed by the rare earth metal borates of the general formula EA M11-x-yM2xEuyB9O16, where EA=Ca, Sr, Ba; M1=Gd, La; M2=Y, Lu, Sc, In and 0xe2x89xa6xxe2x89xa60.5, 0.01xe2x89xa6yxe2x89xa60.4, and M31-r-sYrEusBO3, where M3=Sc,, In, Lu and 0.01xe2x89xa6rxe2x89xa60.99, 0.01xe2x89xa6sxe2x89xa60.15.
In such a plasma display screen, the red pixel has been shifted to obtain a higher color saturation. This does not only affect the red tones but also all intermediate tones on the lines red-green and blue-red, which can be achieved as a result of the increase of the color rendering triangle in the red range. Apart from the red and yellow tones, mainly the magenta range is affected. As a result, many color tones can be reproduced more faithfully, resulting in a visible difference. Besides, the color contrast at bright ambient lighting is improved.
Within the scope of the invention, it is preferred that the phosphor used is the rare earth metal borate BaGd0.8Eu0.2B9O16.
It may alternatively be preferred that the phosphor used is the rare earth metal borate Lu0.5Y0.425Eu0.075BO3.
The invention also relates to a phosphor selected from the group of the rare earth metal borates of the general formula EA M11-x-yM2xEuyB9O16, where EA=Ca, Sr, Ba; M1=Gd, La; M2=Y, Lu, Sc, In and 0xe2x89xa6xxe2x89xa60.5, 0.01xe2x89xa6yxe2x89xa60.4, and M31-r-sYrEusBO3, where M3=Sc, In, Lu and 0.01xe2x89xa6rxe2x89xa60.99, 0.01xe2x89xa6sxe2x89xa60.15.
These and other aspects of the invention will be apparent from and elucidated with reference to two embodiments described hereinafter.